The present invention relates to a method and an apparatus for polishing substrates such as semiconductor wafers.
FIGS. 1(a)-1(c) show a typical example of a process of fabricating an interconnect or wiring circuit on a semiconductor substrate W. In FIG. 1(a), the semiconductor substrate W comprises a base layer 101, an electrically conductive layer 101a, a SiO2 insulating layer 102 in which a contact hole 103 and a groove 104 forming a circuit wiring or interconnect pattern have been formed by lithograph-etching, a barrier layer 105 made of TiN or the like, and a seed layer 107. The semiconductor substrate W is, as shown in FIG. 1(b), plated with metal having a high electrical conductivity, in this example copper, so that a copper layer is formed over the substrate W with the contact 103 hole and the groove 104 being filled with the copper 106. The semiconductor substrate is thereafter subjected to chemical-mechanical polishing to remove the copper layer together with the seed layer 107 and the barrier layer 105 on the surface of the insulating layer 102, leaving the copper 106 in the contact hole 103 and the groove 104 in such a manner that the outer surface of the copper 106 in the hole 103 and the groove 104 is flush with the surface of the insulating layer 102, whereby the copper 106 forms a circuit wiring or interconnect of the substrate.
It is necessary for the polishing process mentioned above to be conducted through several steps in which different polishing conditions are respectively set since the polishing is conducted on a plurality of layers formed on the insulating layer 102 including the copper layer, the seed layer and the barrier layer. In a conventional polishing apparatus, there are provided a plurality of polishing tables suitable for those polishing steps. Accordingly, the conventional polishing apparatus is large, complex in construction, expensive and inefficient or of low throughput.
Further, in a polishing operation of the prior art, a substrate carrier brings the entire surface of a substrate to be polished into contact with the polishing surface of the turntable at a position spaced away from the center of the polishing surface in order to increase the polishing speed. Thus, the polishing surface of the turntable is required to have a large diameter. For example, to polish a substrate having a diameter of 200 mm, the polishing surface is required to have a diameter of about 600 mm. Furthermore, if it is required to make a real-time measurement of a thickness of a surface layer of a substrate which is being polished, a special arrangement of a thickness measuring device (for example, embedding a thickness measuring device into a turntable) must be prepared.